Biocides are chemical compounds, which are toxic to microbial cells and are added to different types of products to prevent the growth of unwanted microorganisms. Reduction in biocidal activity is mostly attributed to the factors such as chemical degradation of biocide, fast dissipation of biocide from application site due to washing out and/or volatilization. The life of any product where biocide is applied, will be more if these biocides are retained in the product/application site for longer period. This extended duration of biocidal activity can be achieved by incorporating biocide in Controlled Release (CR) form. Microcapsule is one of the best controlled release form, wherein an active agent (core material) is surrounded by a polymer film. This is achieved by a process called microencapsulation. Different techniques of microencapsulation are known which include phase separation, solvent evaporation, interfacial polymerization and mechanical methods such as spray drying.
Numbers of reviews on microencapsulation techniques have appeared in literature. (i) Arshady R. (Editor), Microspheres, Microcapsules and Liposomes, Vol. 1 and 2, 1999 and Vol. 6, 2003 Citus Book, UK (ii) Benita S. (Editor), Microencapsulation-Methods and Industrial Applications, 1996, Marcel Dekker Inc., New York; (iii) Madan P. L., Asian J. Pharm. Sci., 9, 1979, p 1; (iv) Thies C. In: Encyclopedia of Polymer Science and Engineering, Vol. 9, Wiley & Sons, New York, 1987, p 724 and (v) Porte H. and Couarrze G., In: Hand book of Powder Technology, 9 (Powder Technology and Pharm. Processes) 1994, p 513). U.S. patents disclosing various microencapsulation methods have been consolidated (Gutcho M. ‘Microcapsules and Microencapsulation Techniques’. New York, Noyes Data, 1976).
Controlled Release Biocides:
Controlled Release (CR) biocides has been the subject of interest to many researchers. CR concept and work was initiated first time on antifouling paints using chloroprene polymer by Prof. N. F. Cardarelli (Cardarelli N. F., Chapter 3 In Controlled Release Technologies: Methods, Theory & Applications, Ed. Kydonieus A. F., 1980, CRC Press Inc., USA). Antifouling marine paint composition containing gelation microcapsules of water-immiscible biocide has been described in U.S. Pat. No. 4,253,877. Yet another U.S. Pat. No. 5,378,413 describes preparation of gelatin microcapsules containing fouling reducing agents and their use in paint system. Another report describes extended control of marine fouling using formulation of microencapsulated organometallic biocide and vinyl rosin paint. (Porter R. and Miale J. B., Appl. Biochem. and Biotech., 9 (1984), p 439-445 (CA 102:162052)).
Apart from CR antifouling formulations there have been very few reports on CR of other biocides. Biocide namely 4,5-dichloro-n-octyl-3-isothiazolinone (DCOI) can be encapsulated in a variety of polysiloxane matrices using sol-gel chemistry (Ghosh T. and Nungesser E. N., Proc. Int. Symp. Control. Rel. Bioact. Mater. 25 (1998), p 324). The skin sensitization potential of active agent (3-isothiazolone) in loci such as water-based marine antifouling paint of decorative is reduced by encapsulating the active agent in polyurea (.EP 679333 (1995), (CA 123: 332738)). The fungicide tebuconazole and chlorothalonil were successfully incorporated into polyvinylpyridine (PVPy) and polyvinylpyridine-co-styrene nano particles (Liu Y. et. al., J. Appl. Poly. Sci, 79 (2001), p 458-465).
U.S. Pat. No. 4,915,947 describes preparation of microencapsulated phytotoxic fungicides using crosslinked polytirea or polyamide to provide an effective agent for direct foliar application to control fungal diseases on crops. Urea-formaldehyde (UF) and/or melamine formaldehyde (MF) resins have been used to prepare microcapsules of fungicide namely 3-Iodo-2-propynylbutyl carbamate. These microcapsules when incorporated into exterior latex paint and applied onto rubberwood panels on exposing to the environment showed longer protection from discoloration. (Ibrahim W. A. et. al., Pertanika 12 (1989) p 409-412 (CA 114:25832)). The acrylic latex exterior paint containing microcapsules of fungicides 2,3,5,6-tetrachloro-4-methylsulfonylpryidine and tetrachloroisophthaonitrile have been reported to show good mildew protection (Noren G. K. et. al., J. Coatings Tech. 58 (1986), p 31-39 (CA 104: 188225)).
Another patent describes encapsulation of biocide using MF resin and their use in coating material like plaster having silicate, mineral or polymer resin binder or a primer based on a silicate or polymer resin binder (Patent WO 2004000953). The patent describes preparation of microcapsules containing Zinc Pyrithione using MF resin but does not specify the size of the microcapsules obtained. Japanese patent (No. JP 2003104802) describes antibacterial aqueous dispersion compositions containing microencapsulated dithioles or 2,2-dibromo-3-nitrilopropionamide and other microbiocides like Zinc Pyrithione. The patent does not describe preparation of microcapsules of Zinc Pyrithione but mentions that Zinc Pyrithione is added to composition containing microcapsules of other compounds as mentioned above.
Microcapsules Prepared by Solvent Evaporation:
There are many reports in the literature related to preparation of microcapsules by solvent evaporation techniques. These reports are documented in the references mentioned in the introduction part of the section “Prior art references and background of the invention”. Microencapsulation by solvent evaporation is carried out involving oil in water, water in oil or water in oil in water type emulsion systems.
U.S. Pat. No. 5,725,869 describes preparation of microcapsules containing agricultural materials by solvent evaporation method. Microcapsules described in this patent have a size of between about 3 and about 300 microns in diameter. The complex water in oil in water or simple water in oil emulsion system has been used to prepare polystyrene, poly(methyl methacrylate), ethyl cellulose, poly(vinyl chloride) microcapsules containing aqueous solution of gelatin (Kentepozidou A. and Kiparissides C. J. Microencapsulation 12 (1995) p 627-638). Solvent evaporation method involving such double emulsion system (water in oil in water) has been used to prepare microcapsules of polystyrene containing corrosion inhibitors (Anne Mac et al., J. Microencapsulation 6 (1989) p 361-367) poly(methyl methacrylate) microcapsules containing highly water soluble drug (Alex R. and Bodmeier R., J. Microencapsulation 7 (1990) p 347-355) or water soluble dyes (Zydowicz N. et al., Poly. Bull. 47 (2002) p 457-463, CA 136:341624).
Biocides play an important role in variety of applications. However reduction in biocidal activity due to factors such as chemical degradation of biocide and/or fast dissipation of biocide from the application site due to reasons like washing out with water is a problem which leads to decrease in period of effectiveness of biocide.
In the prior art there is no existence of any product like polymer microcapsules of biocide selected from Irgarol and Zinc Pyrithione particularly with specified particle size or size range.
Thus to satisfy the need to prolong the life of biocide, present invention provides microcapsules of Irgarol and Zinc Pyrithione with controlled particle size distribution in the range of 1-100 microns, which are effective algaecide and fungicide respectively.